Steam purge indicator method and apparatus



Oct. 3, 1961 w. BULKLEY ET AL 3,002,372

STEAM PURGE INDICATOR METHOD AND APPARATUS Filed March 51, 1958 IN VENTORS William L Bulk/8] BY Dan Smifl) ut-$09M ATTORNEY 3,002,372 STEAM PUR'GE INDICATOR METHODAND APPARATUS William L. Bullkley, Munster, Ind., and Dan Smith, Chicago, lll., assignors to Standard Oil Company, Chicago,

111., a corporation of indiana Filed Mar. 31, 1958, Ser. No. 724,995 13 Claims. (Cl. 73-29) This invention relates to method and apparatus 'for 'de: tel-mining a variable composition comprising a mixture of readily condensable gas and relatively non-condensable gas. In a more specific sense, the invention relates to a system for indicating the end point of steam purging operations.

. In petroleum refining, it is often necessary to remove non-condensable combustible and/ or combustion supporting gases from a system before introducing other substances into the associated apparatus. If such gases re main in the system they may cause corrosion, may poison catalyst, or may constitute a fire or explosion hazard during a subsequent operation within the system.

Steam purging of process vessels and the like is one method commonly employed to purge such gases below the level at which combustion resulting in explosion or detonation could occur. Normally, the practice'has been to discontinue steam purging upon a show of steam at the exhaust, the assumption being made that steam has completely displaced the non-condensables from the system. However, this method does not give a reliable indication of the removal of the combustible or combustionsupporting gases because such gases are not necessarily displaced first by the flow of steam from the exhaust end of the system. Thus the'gases are often exhausted in partial admixture with the purging steam and the mere show of steam, therefore, does not indicate that the system has been completely purged of the non-condensable gases.

We have made tests of steam exhausting into the atmosphere and based on visual observations and photographs, there is little difference in the appearance of pure steam on the one hand and steam-air mixtures on the other, unless the air content of the steam exceeds 50%. Such an indication is of little value;

. Many systems have heretofore been proposed for measthing the proportion of condensables in a steam purging operation for indicating the safe end point. One such system measures change in volume at constant pressure. Apparatus conventionally used in'such system consists essentially of a glass bulb enclosed in a sheet metal case and insulated against heat loss, the upper part of the enclosed bulb being graduated.

A stop-cock is provided at the upper end of the glass bulb and a two-Way stop-cock at the lower end of the bulb permits connection at the bottom either to a Waterfilled leveling bottle or to the atmosphere. Air is displaced from the bulb by water from the leveling bottle. The upper stop-cock is then connected to a sample point on the steam purged vent pipe, preferably with heavywalled rubber tubing.

The upper stop-cock is opened to displace the water from the bulb into the leveling bottle and as the water level reaches the lower two-way stop-cock, the latter is turned to permit the sample of purged gas to flow freely through the apparatus for not less than about five minutes. A sample is thentrapped Within the glass bulb by operating both upper and lower stop-cocks. Water from the leveling bottle enters the indicator bulb to replace the condensed vapor. The non-condensable gas volume remaining Within the bulb is read from the calibrated scale on the bulb. However, before making the reading, the water levels within the bulb and leveling bottle are made equal by adjusting the latter, thereby assuring atmospheric pressure in the bulb. It will be apparent that such an apparatus is fragile and that the systern is complicated so as to require considerable technical skill and judgment in its operation.

An important object of the invention accordingly is to provide a system which avoids all of the complications and difficulties inherent in the volume measuring kind of apparatus. A more specific object is to provide a system wherein it is not necessary to measure the volume or" the non-condensables directly. A further object is to provide a simple and relatively inexpensive portable apparatus which is both durable and accurate and which can be used to make the determinations of non condensa bles by simply noting the pressure Within a sample cylinder before and after condensation of a confined 'volume of exhaust steam purge effiuent.

It is also a principal-object of this invention to provide an apparatus for the determination of the amount of readily condensable gas or the percentage of non-condensables present in a mixture. A further object of the invention is to provide a method and apparatus for determining the end point at which all non-condensable gases have been removed from a system in a steam purging operation. A more specific object of the invention is to provide a steam purge indicator of simplified construction and operation and wherein a simple pressure measurement will provide an indication of the non-condensables in the. system being purged.

Briefly, according to the invention, a sample of vent steam is passed through a chamber, the chamber being provided with inlet and outlet valves at opposite ends thereof. The temperature within the chamber is 'meas ured, and when equilibrium conditions are indicated by a constant temperature reading, the inlet and outlet valves on the sampling chamber are quickly closed, in that order, to trap a sample of purge gases. within the chamber at atmospheric pressure.

The chamber containing the trapped sample is cooled rapidly to a preselected temperature, preferably about F., by, for example, immersing in water. The cooling reduces the pressure Within the chamber by condensing the condensable water vapor. The pressure indicatecl by a gauge communicating With the chamber is a measure of non-condensables in the "vent gas.

Since the vapor pressure of water at 100 F. is about 2 inches Hg, 100% steam in the sample chamber will produce a vacuum numerically equal to 2 inches Hg less than the total barometric pressure. Thus, for example, if the local barometric pressure is equal to 30 inches Hg, the vacuum gauge reading will be 28 inches Hg. If less, vacuum is observed, for example, 26 inches Hg, this indicates the presence of non-condensables. Accordingly, the percent non-condensables can be indicated as a function of the vacuum gauge reading and a limiting vacuum reading can be specified beyond which the purge may be considered satisfactory. If the actual percentage of noncondensables present need be known, it may be calculated from data obtained With the instrument by methods well known to those skilled in the art.

The device may be calibrated quickly in the field by.

connecting to a steam line. This will indicate the gauge reading for 100% steam thereby eliminating the need for-- determining the local barometric pressure. This will also serve as a leak test for the device.

In addition to simplifying the calculation and eliminat ing the need for referring to a barometer, the initial measurement on steam, free from non-condensables, pro vides a leak test of the apparatus wherein tightness is. shown by maintainence of the low pressure reading. Further, this check has the elfect of measuring the bare! 3 metric pressure with the instrument gauge thereby compensating for minor inaccuracies in the gauge.

Further advantages and details of the construction of our apparatus will be described by reference to the accompanying drawings wherein:

FIGURE 1 is a schematic elevation illustrating the invention; and

FIGURE 2 illustrates an automatic recording embodiment of the invention.

Referring to FIGURE 1, the sample cylinder is provided with an upper inlet valve 11 and a lower outlet valve 12, each communicating with the interior of the cylinder 10. The cylinder 10 is or a shape which allows free passage of purging gases throughout its interior with out any holdup by occlusion or otherwise. The lower end of the cylinder 10 is provided with a tripod support 13. The upper end of the apparatus is provided with a carrying handle 14-.

The pressure gauge 15 is in communication with the cylinder 10 below the inlet valve 11 and a thermometer well 16 projects through a wall of the cylinder 19. The outlet valve 12 is adjusted to drain fluids from the cylinder 10 and to maintain atmospheric pressure therein during the sampling.

When it is desired to make a test, exhaust steam from a purging operation is charged by line 17 to the cylinder 10 through the inlet valve 11 while the outlet valve 12 is maintained in an open position. The condensation temperature of the exhaust steam, i.e. the point at which no further reduction in pressure is observed, is measured in well 16. The purge gases are permitted to flow through the device until the temperature as indicated by the thermomcter 18 is constant. The inlet valve 11 is first closed and then the outlet valve 12 is also closed thereby trapping a uniform sample of exhaust steam at atmospheric pressure. I

The cylinder 16 is cooled by natural convection or the cooling rate may be accelerated by spraying with cooling fluid or immersing the cylinder 1% in such a bath 1.6:: as schemactially shown in FIGURE 1.

If low ambient temperatures require excessive time to obtain the equilibrium condensation temperature within cylinder 10, an insulated container (not shown) can be provided into which cylinder 16 can be inserted during the flow of the sample into the device. After equilibrium condensation temperature is reached and valves 11 and 12 have been closed, the cylinder 14) is removed from the insulated container and cooled as described. if desired, the tripod support 13 may be modified so as to support the insulated container.

When the measurement of non'oondensables in steam is desired for the control of a continuous process, for example, or for other reasons, remote indication and/or continuous recording of such measurements may be desirable. Such a device is illustrated in FIGURE 2 and can be made completely automatic.

In the embodiment of FIGURE 2, the steam-air mixture is admitted through valve 11 and exhausted at the bottom of the chamber 10 through valve 12. A portion of the same steam is admitted to coil 22 surrounding the chamber 10, and connected to the chamber 10 through two-way valve 20.

Cycle timer 21 controls valves 11, 12 and in such a manner that flow into the chamber 10 and coil 22 continues for a preselected time sufiicient to bring the chamber It! to equilibrium temperature. The cycle timer 21 then closes valves 11 and 12 to trap the sample within the chamber 10 and at the same time actuates two-way valve 20 to flow cooling water from line 23 through the coil 22 in place of the steam mixture.

' Absolute pressure transmitter 24, coupled with receiver 25, which may be indicating or recording or both, provides continuous record of the pressure in chamber 10.' As described with respect to FIGURE 1, the pressure within the chamber 10 after cooling to the preses oasra equipment, generally.

3. lected temperature is a measure of the non-condensables in the stream introduced to the test chamber 19.

if desired, receiver 25 can be made a recorder-controller which will sense the equilibrium hot condition t the chamber 10 and actuate the cycle timer 21 so that it may follow through the cycle described above.

The system in accordance with the invention is particularly advantageous when used to determine the safe oxygen content of stearn-air mixtures used in operations such as the regeneration of desulfurization reactors during reforming operations orfor determining the safe end point when purging combustion-supporting gases from process However, the devicesv may be readily adapted to a control operation involving the de termination of non-condensables and condensables in a given system. It is also contemplated that anon-condensable purge gas may be used to purge a condensable gas or vapor from a system in which case the end point in the purging operation is determined by the presence of 100% non-condensables in the exhaust from the system being purged. 1 Although the invention has been described in terms of a preferred embodiment which has been set forth in some detail, it should be understood it is by way of illustration only and that the invention is not necessarily limited thereto. Alternative embodiments of the invention will become apparent to those skilled in the art in view of the accompanying description and accordingly,

- modifications in the invention are contemplated without departing from the spirit thereof.

What we claim is:

l. A method for measuring and indicating the presence of non-condensable gases in admixture with a condensabIe gaseous medium which comprises trapping a selected volume otsaid admixture under atmospheric pressure, cooling said trapped volume to a preselected temperature well below the condensation temperature of the said gaseous medium, and indicating the pressure of said volume at said preselected temperature as a measure of the trapped non-condensable gases.

2. The method of claim 1 wherein the said condensable gaseous medium is steam and the preselected temperature is about F.

3. A method for quantitatively indicating the presence of non-condensable gases in admixture with a condensable gaseous medium which comprises trapping a sample of said admixture within a container under atmospheric pressure, cooling said container to a pre-determined temperature well below the condensation temperature of the said gaseous medium, and indicating the pressure within said container as a measure of the non-condensable gases present in the admixture.

4. A device for indicating the presence of non-condensable gases in an admixture with steam which comprises a sampling vessel for said admixture, temperature indicator means on said vessel, pressure indicator means for said vessel, an inlet valve positioned on and communicating within said vessel, an outlet valve positioned on the lower end of said vessel, a cycle timer valve-control device sequentially closing said inlet valve and said outlet valve, respectively, and fluid cooling bath means for immersing said vessel.

5. A device for indicating the end point of steam purging operations which comprises a portable vessel, means for indicating the temperature within said vessel, inlet valve means on one end of said vessel, outlet valve means on the other end of said vessel, a cooling bath means adapted to receive said vessel, handle means on said vessel for manipulating said vessel so as to submerge it within said cooling bath, means for indicating pressure in said vessel, and cycle timer means for sequentially closing said inlet and outlet valve means.

6. A device for indicating the presence of non-condensable gases in a condensable gaseous medium which comprises a portable container, means for indicating the pressure within said container, inlet valve means on said container, outlet valve means on said container, means about said container for controlling the temperature thereof, and means for automatically controlling said inlet valve means and said outlet valve means and wherein said means for controlling the temperature of said container includes coil means surrounding said container and through which heat exchange media flow.

7. A device for indicating the presence of non-condensable gases in a condensable gaseous medium which comprises a portable container, means for indicating the pressure within said container, inlet valve means on said container, outlet valve means on said container, means about said container for controlling the temperature thereof, and wherein said means for indicating the pressure comprises an absolute pressure transmitter and a pressure recordercontroller, and a cycle timer means for controlling said inlet and outlet valve means, said cycle timer means being actuated by said recorder-controller.

8. An automatic steam purge indicator apparatus comprising a sample trapping vessel, valved inlet means on said vessel, valved outlet means on said vessel, pressure sensitive means connected to said vessel, means for heating said vessel, means for cooling said vessel, and cycle timer means actuated by said pressure sensitive means to control said inlet and outlet valves and said heating and cooling means.

9. The apparatus of claim 8 wherein said cycle timer is adapted to close said outlet valve after closing said inlet valve.

10. The apparatus of claim 8 wherein said heating means comprises coil means about said vessel adapted to receive a portion of the steam being sampled, and wherein said means for cooling said vessel includes a source of cooling fluid which is flowed through said coil means.

11. A device for indicating the presence of non-condensable gases in a condensable gaseous medium which comprises a portable container, means for indicating the pressure Within said container, inlet valve means on said container, outlet valve means on said container, means about said container for controlling the temperature there of, and wherein said means for indicating the pressure comprises an absolute pressure transmitter communicating with said container and a pressure receiver remote therefrom, and a cycle timer means for controlling said inlet and outlet valve means, said pressure receiver being a recorder-controllerarranged to actuate the cycle timer means. 7

12. An apparatus for measuring and indicating the presence of noncondensable gases in admixture with a condensable gaseous medium which comprises means for trapping a selected volume of said admixture under atmospheric pressure, means for cooling said trapped volume to a preselected temperature well below the condensation temperature of the said gaseous medium, and means for indicating the pressure of said volume at said preselected temperature as a measure of the trapped noncondensable gases.

13. An apparatus for quantitatively indicating the presence of noncondensable gases in admixture with a condensable gaseous medium which comprises means for trapping a sample of said admixture within a container under atmospheric pressure, means for cooling said container to a predetermined temperature well below the condensation temperature of the said gaseous medium, and means for indicating the pressure within said container as a measure of the noncondensable gases present in the admixture.

References Cited in the file of this patent UNITED STATES PATENTS 2,160,004 Stamm May 30, 1939 2,299,899 Houghland Oct. 27, 1942 2,538,710 Smith Jan. 16, 1951 

